Carbohydrate oxidation from a drink during running compared with cycling exercise.

UNLABELLED: Current recommendations for CHO intake in the field for all modes of endurance exercise are largely on the basis of laboratory studies that measured oxidation of ingested CHO. However, the majority of these laboratory studies used cycling as the mode of exercise, and it is not known whether these results can be extrapolated to running. PURPOSE: the purpose of this study was to investigate exogenous CHO oxidation from a CHO drink during moderate-intensity running (RUN) compared with cycling (CYCLE). METHODS: eight athletes with comparable CYCLE and RUN training backgrounds (mean ± SD: age = 37 ± 7 yr, weight = 75 ± 7 kg, height = 1.77 ± 0.05 m; V˙O2max CYCLE = 63 ± 3 mL·kg·min, V˙O2max RUN = 65 ± 4 mL·kg·min) performed four exercise trials in random order. The trials consisted of either running or cycling at approximately 60% of the exercise specific V˙O2max for 120 min while receiving either a CHO drink (2:1 glucose-fructose blend; 1.5 g·min) or a similar volume of plain water (WAT; 675 mL·h). RESULTS: the set workload elicited similar relative exercise intensities of 59.7% ± 2.0% and 59.2% ± 1.9% V˙O2max for RUN and CYCLE, respectively. Peak and average exogenous CHO oxidation rates were not significantly different between RUN and CYCLE trials and showed a similar time course (peak at 120 min = 1.25 ± 0.10 vs 1.19 ± 0.08 g·min, respectively, P = 0.13; average over final hour = 1.14 ± 0.10 and 1.11 ± 0.11 g·min, respectively, P = 0.94). Furthermore, total fat oxidation rates were higher during RUN compared with CYCLE. The difference was significant with ingestion of WAT (P = 0.02) and failed to reach statistical significance with CHO (P = 0.09). CONCLUSIONS: this study demonstrates that exogenous CHO oxidation rates are similar between prolonged running and cycling at a similar relative moderate intensity. These data suggest that previous exogenous CHO oxidation results from cycling studies can be extrapolated to running.

Oxidation of solid versus liquid CHO sources during exercise.

UNLABELLED: The ingestion of CHO solutions has been shown to increase CHO oxidation and improve endurance performance. However, most studies have investigated CHO in solution, and sporting practice includes ingestion of CHO in solid (e.g., energy bars) as well as in liquid form. It remains unknown whether CHO in solid form is as effectively oxidized as CHO in solution. PURPOSE: To investigate exogenous CHO oxidation from CHO provided in either solid (BAR) or solution (DRINK) form during cycling. METHODS: Eight well-trained subjects (age = 31 ± 7 yr, mass = 73 ± 5 kg, height = 1.79 ± 0.05 m, VO2max = 69 ± 6 mL·kg−¹·min−¹) cycled at 58% ± 4% VO2max for 180 min while receiving one of the following three treatments in randomized order: BAR plus water, DRINK, or water. The BAR and DRINK was delivered glucose + fructose (GLU + FRC) in a ratio of 2:1 at a rate of 1.55 g·min−¹, and fluid intake was matched between treatments. RESULTS: During the final 2 h of exercise, overall mean exogenous CHO oxidation rate was −0.11 g·min−¹ lower in BAR (95% confidence interval = −0.27 to 0.05 g·min−¹, P = 0.19) relative to DRINK, whereas exogenous CHO oxidation rates were 15% lower in BAR (P < 0.05) at 120, 135, and 150 min of exercise. Peak exogenous CHO oxidation rates were high in both conditions (BAR 1.25 ± 0.15 g·min−¹ and DRINK 1.34 ± 0.27 g·min−¹) but were not significantly different (P = 0.36) between treatments (mean difference = −0.9 g·min−¹, 95% confidence interval = −0.32 to 0.13 g·min−¹). CONCLUSIONS: The present study demonstrates that a GLU + FRC mix administered as a solid BAR during cycling can lead to high mean and peak exogenous CHO oxidation rates (91 g·min−¹). The GLU + FRC mix ingested in the form of a solid BAR resulted in similar mean and peak exogenous CHO oxidation rates and showed similar oxidation efficiencies as a DRINK. These findings suggest that CHO from a solid BAR is effectively oxidized during exercise and can be a practical form of supplementation alongside other forms of CHO.

CHO oxidation from a CHO gel compared with a drink during exercise.

UNLABELLED: Recently, it has been shown that ingestion of solutions with glucose (GLU) and fructose (FRC) leads to 20%­50% higher CHO oxidation rates compared with GLU alone. Although most laboratory studies used solutions to deliver CHO, in practice, athletes often ingest CHO in the form of gels (semisolid). It is currently not known if CHO ingested in the form of a gel is oxidized as effectively as a drink. PURPOSE: To investigate exogenous CHO oxidation from CHO provided in semisolid (GEL) or solution (DRINK) form during cycling. METHODS: Eight well-trained cyclists(age = 34 ± 7 yr, mass = 76 ± 9 kg, VO2max = 61 ± 7 mL·kg−¹·min−¹) performed three exercise trials in random order. The trials consisted of cycling at 59% ± 4% VO2max for 180 min while receiving one of the following three treatments: GEL plus plain water, DRINK, or plain water. Both CHO treatments delivered GLU plus FRC in a ratio of 2:1 at a rate of 1.8 g·min−¹ (108 g·h−¹). Fluid intake was matched between treatments at 867 mL·h−¹. RESULTS: Exogenous CHO oxidation from GEL and DRINK showed a similar time course,with peak exogenous CHO oxidation rates being reached at the end of the 180-min exercise. Peak exogenous CHO oxidation rates were not significantly different (P = 0.40) between GEL and DRINK (1.44 ± 0.29 vs 1.42 ± 0.23 g·min−¹, respectively). Furthermore, oxidation efficiency was not significantly different (P = 0.36) between GEL and DRINK (71% ± 15% vs 69% ± 13%, respectively). CONCLUSIONS: This study demonstrates that a GLU + FRC mixture is oxidized to the same degree then administered as either semisolid GEL or liquid DRINK, leading to similarly high peak oxidation rates and oxidation efficiencies.

Alpha and gamma tocopherol metabolism in healthy subjects and patients with end-stage renal disease.

BACKGROUND: The metabolism of alpha and gamma tocopherol, the major components of vitamin E, have not been studied in uremic patients. The major pathway of tocopherol metabolism is via phytyl side chain oxidation, leaving carboxyethyl-hydroxychromans (CEHC) as metabolites. Alpha and gamma CEHC are water soluble, renally excreted, with known potent anti-inflammatory and antioxidative properties. METHODS: We examined serum alpha and gamma tocopherol and respective CEHC concentrations in 15 healthy subjects and 15 chronic hemodialysis patients. RESULTS: Serum alpha tocopherol levels were similar in hemodialysis patients (12.03 +/- 1.34 microg/mL) and healthy subjects (11.21 +/- 0.20 microg/mL), while serum gamma tocopherol levels were significantly greater in hemodialysis patients (3.17 +/- 0.37 microg/mL) compared to healthy subjects (1.08 +/- 0.06 microg/mL, P < 0.0001). Serum alpha and gamma CEHC levels were tenfold and sixfold higher in hemodialysis patients compared to healthy subjects, respectively (both P < 0.0001). Serum alpha and gamma tocopherol levels and CEHC metabolites were also measured after supplementation of alpha- or gamma-enriched mixed tocopherols in both hemodialysis patients and healthy subjects. Tocopherol administration resulted in modest or nonsignificant changes in serum tocopherol concentrations, while markedly increasing serum CEHC concentrations in both healthy subjects and hemodialysis patients. Hemodialysis resulted in no change in the serum alpha or gamma tocopherol concentrations while decreasing serum alpha CEHC and gamma CEHC levels by 63% and 53%, respectively (both P = 0.001 versus predialysis). Fourteen-day administration of gamma-enriched but not alpha tocopherols lowered median C-reactive protein (CRP) significantly in hemodialysis patients (4.4 to 2.1 mg/L, P < 0.02). CONCLUSION: First, serum alpha and gamma CEHC accumulate in uremic patients compared to healthy subjects; second, supplementation with tocopherols dramatically increases serum CEHC levels in both healthy subjects and hemodialysis patients; and, finally, CEHC accumulation may mediate anti-inflammatory and antioxidative effects of tocopherols in hemodialysis patients.